初始浓度对南海珊瑚泥沉积浊液面沉速特性影响试验研究

Experimental study on effects of initial concentration on settling velocity characteristics of turbid surface of South China Sea coral mud

珊瑚泥是由细粒珊瑚碎屑组成的钙质软泥,在南海岛礁的吹填地基中因颗粒分选以夹层形式分布。在整个吹填场地形成过程中,珊瑚泥的沉积特性会对吹填后形成岛礁的地基稳定性产生一定影响。因此,从影响地基稳定性最初阶段的吹填沉积特性出发,探求初始浓度对珊瑚泥浊液面沉速特性影响。利用扫描电镜观察絮凝体尺寸,根据Stokes定律推得浊液面在等速沉积阶段的理论沉速,并与颗粒组成相近的海相沉积土和同塑性指数的芜湖粉质黏土的沉积特性展开对比分析。试验结果表明:三种土浊液面出现的高度随初始浓度减小而减小;在等速沉积阶段,浊液面沉速随初始浓度增大而减小,其变化逐渐减缓并趋于稳定。区别在于,珊瑚泥浊液面出现时间最早,其沉速远高于其他两种土,等速沉积阶段所用时间仅为其他两种土的1/3,且初始浓度对珊瑚泥等速沉积时间的影响最为明显。最后推导得到了初始浓度与浊液面沉速关系公式,这对于南海海域吹填施工及地基的安全稳定具有一定的现实意义。

The coral mud is the calcareous ooze composed of fine-grained coral debris, which is distributed in the form of sandwich by particle sorting. During the formation process of an entire filling site, the sedimentary characteristics of the coral mud will have influences on the foundation stability after the filling. Therefore, from the sedimentary characteristics at the initial stage for the stability of the foundation, the effect of the initial concentration on the surface velocity of coral mud turbid surface is explored. The size of flocculation is observed by using the scanning electron microscope(SEM). The theoretical sedimentation velocity of the turbid surface at the constant velocity sedimentation stage is deduced according to the Stokes formula. Through the sedimentation tests on the coral mud, marine sedimentary soil with similar particle composition and Wuhu silty clay with the similar plastic index, the sedimentary characteristics of the three sediments are compared and analyzed. The results show that the height of turbid surface decreases with the decrease of the initial concentration during the sedimentary processes of three kinds of soil. At the constant velocity sedimentation stage, the settling velocity of turbid surface decreases with the increasing initial concentration, and the change is gradually mitigated and stabilized. The difference is that the settling velocity of coral muddy surface appears at the earliest time, and its sedimentation rate is much higher than that of the other two kinds of soil. The time at the constant velocity sedimentation stage is only 1/3 of that of the other two kinds of soil, and the initial concentration has the most obvious effect on the constant velocity sedimentation time of coral mud. Finally, the relationship between the initial concentration and the turbid surface is obtained. It is of a practical significance for the construction of dredge fill and safety and stability of foundation in South China Sea.